Many elements and systems depend on or benefit from availability of an accurate clock. Cost-effectively getting sufficient clock accuracy to separated locations is often a very difficult challenge. For instance, even if wired connectivity can be established between locations, accurate and cost-effective distribution of clock information is often complex and costly. In addition, maintaining and verifying that clock accuracy in the presence of failures or other disturbances further increases the challenges. Finally, clock accuracy requirements along with the need to certify, continually monitor, and provide traceable results are becoming increasingly more stringent.
Wireless cellular systems include base stations and end nodes. To support time-division duplexing, improve efficient use of time and frequency resources, allow seamless handovers to different cells, reduce inter-symbol interference, and provide many other features and functionalities, the clocks of the base stations in a cellular system should be synchronized. As radio technology continues to improve, including migrating from early versions of 4G LTE, to 4G LTE-A, to 5G, and advanced capabilities are introduced such as precision location services for public safety, the synchronization requirements continue to become more stringent. This includes movement from frequency-only requirements, to timing phase requirements at the base station antenna approaching and even exceeding 35 nanoseconds (nsec). Unfortunately, even if able to initially or during non-fault conditions achieve such accuracy, impairments like oscillator drift and phase noise contribute to errors in time synchronization that decrease efficiency. Further compounding synchronization challenges, the number of base stations needed to support increasing data demands supported by 5G networks, WiFi networks, and other data delivery networks will significantly increase beyond the number of base stations that exist today.
In some previous and existing systems, the Institute for Electrical and Electronic Engineers (IEEE) 1588 Precision Time Protocol (PTP) is used to synchronize base stations via wired connections, typically called backhaul, to the base stations. However, to achieve predictable and accurate results, implementation of PTP also requires deployment of IEEE 1588 hardware at each node between the base station and a master clock which is often located far away within the network. Including the fact that wireless network operators often do not have control of all the nodes providing backhaul service, it is also often expensive to equip all nodes even when the control is available. Even when equipped, accuracy at the base station antenna to the level of approximately 1.5 microseconds (μsec) is typically the best that can be achieved over a metro-sized area, with worse performance as the area is larger. That level of performance does not meet the timing synchronization needs of next generation wireless networks.
In some previous and existing systems and techniques synchronization relies on a Global Positioning System (GPS) receiver at each base station to set the clocks at the base stations. Where GPS receivers provide higher accuracy than IEEE 1588 to the level of approximately 50 nsec, GPS receivers may not provide sufficient clock synchronization to support 5G and other demanding systems in a cost efficient and reliable manner, including in various failure modes. Moreover, service providers in some countries may not be guaranteed GPS service. GPS signals can also be vulnerable to jamming attacks, are ineffective inside buildings and structures, and can be vulnerable to solar flares. Therefore, either relying on GPS receivers that are already in place, or performing expensive upgrades to base stations to equip cases where GPS receiver are not already in place is inadequate to meet the timing synchronization and reliability needs of next generation networks.
In general, existing timing synchronization accuracy of current systems may therefore be insufficient for 5G and other new technologies. Thus, a cost efficient means of providing accurate timing synchronization has great value for existing and upcoming wireless networks, as well as for enabling future technologies and applications.